Static frequency changer



June 21, 1949. R, w. JONES 'STATIC FREQUENCY CHANGER Filed June 26, 1947 INVENTOR. Rby W. Jones BY ATTORNEY Patented June 21, 1949 3.Claims. r1 Thepresent-inventi n relates in general to static frequency changer systems and more particularly to a static frequency changer which is adapted tothe production-of audio frequency signals suitable for use as dialtand busy tone-sig-' nals in an automatic telephone system.

Static frequency 'chang'ersusing two transformers with a magneticbias are wellknown in the art. J Applicant believes his, invention discloses a novel'ineans. for imparting:..-the magnetic bias:

to the transformer cores and for causing the output voltage to be a desired multiple of the frequency of the input voltage.

An object of this invention is a new and imprOVed method of increasing the frequency of an alternating current.

A feature of the invention is the provision of a resonant circuit which is tuned to a particular harmonic of the fundamental frequency,

Another feature of the invention is the provision of a direct current magnetic biasing circuit which includes at least a part of the aforementioned resonant circuit.

Other objects and features of the invention will become apparent upon a further perusal of the specification taken in conjunction with the accompanying drawings in which:

Fig. 1 is a schematic diagram of the invention.

Fig, 2 graphically represents the input voltage and the output voltage wave forms.

It is to be understood that the curves of Fig. 2 are not necessarily correct insofar as phase relation is concerned, the input voltage curve A being shown primarily to indicate the frequency relationship which exists between the two curves.

Referring now to Fig. 1, an alternating current of a certain frequency from source is passed through the primary windings l and 2 of the two transformers T1 and T2 which windings are connested in series aiding. The secondary windings 3 and 4 of these transformers are connected in series opposing. The cores of transformers T1 and T2, which are constructed of standard magnetic iron, are magnetically biased in opposite directions due to the direct current flowing from battery in, through resistance 9, primary winding 6 of transformer T3, and secondary windings 3 and 4 to ground. The magnetic bias produced in each of the two transformer cores of T1 and T2 by this direct current flow is induced in opposite directions due to the series opposing nature of the secondary connection. This magnetic bias is preferably of such a value as to substantially saturate the transformer cores, that is, to operate the cores substantially above the knee of the 'asaturation curve. .Q'Itns.sapparentithatzcmanigwoti'cular half cycle; ofz-atheiz impmseedaaltemntin current, the. magneticifiuxxproduceditherehywill ;:be in suchza direction; as :to aid thermagnetleibiaswing fluxainsone.transformerwandippnoajahe me pznetic; biasing flux in Ethei'bther itransfmner resultant voltage appearingc-anrossnhe combiaed secondariesv of the twcetrahsformer af-llir-iand'iiflz is obtained by subtracting t the mountainous values-t voltage :rappearingtaormsreacimsmndwary. 'I'l:1is--results-in thewamtellatinni tinndamental frequency, that is, the frequency at the source and leaves a large second harmonic plus voltages of the higher harmonics;

The capacitance element 5 and the inductance of windings 3, 4 and 6 are of such valueeas to form a resonant circuit. In the present case, cycle commercial power was used as the source I and the resonant circuit was tuned to theheighth harmonic or 480 cycles. The 480 cycle output wave form is shown in Fig. 2 as curve; B. It will be noted that curve B shows a logarithmicidecay in voltage amplitude which is characteristic of resonant circuits. This indicates that the resonant circuit receives a currentsurge for each half cycle of the impressed signal. This type of wave form produces a characteristic low-pitched tone which is particularly useful for dial and busy tone in a telephone exchange.

The coupling transformer T3 serves two purposes. First, it serves to step the output voltage down to a value suitable for use in ,a telephone exchange or other application for which :the apparatus is to be used, second, it, together with resistance 9, serves to isolate the battery from Ti and T2 so that the battery will not constitute a short circuit for the secondary windings 4 of Ti and T2. The capacitance element 8 is merely a. by-pass condenser and resistance 9 acts as a D. C. load resistance.

While I have shown what at present'ds considered to be the principal embodiment of my invention, it is to be understood that numerous modifications in the details of construction and the combination and arrangementjofrparts may be resorted to without departing from the true spirit and scope of the invention as set forth in the subjoined claims.

What is claimed is:

1. In a static frequency changer, two trans-v formers each having a magnetic core, a primary winding, and a secondary winding, said primary my!) n P s to cause alternatin current to flow in said primary windings, a direct current source connected to cause direct current to flow in said secondary windings to thereby induce a unidirectional magnetic bias in said transformer cores, 3, capacitance element connected across said secondary windings which, in combination with said secondary windings,',.forms a resonant circuit, a load circuit, the voltage appearing in said load circuit having a frequency corresponding to the natural period of oscillation of said resonant circuit.

2. In a frequency changer, two transformers each having a magnetic core, a primary, and a secondary winding, said primary windings being connected in series aiding and said secondary windings being connected in series opposing, an alternating current source connected to cause alternating current to flow through said primary windings, a direct current circuit for causing direct current to flow through said secondary "windings to thereby induce a unidirectional magneticbias in said transformer cores, 9, capacitan'ce element connected across said secondary windings which, in combination with said secondary windings, forms a resonant circuit, a load circuit including a third transformer having primary and secondary windings, the primary winding of said third transformer forming a part of said direct current circuit, the voltage appearing across the secondary winding of said third transformer having a frequency corresponding to the 4 natural period of oscillation of said resonant circuit.

3. In a frequency multiplier, a pair of transformers, a source of alternating current, a source of direct current, an output transformer, a circuit including the alternating current source and the primary windings of said pair of transformers, a second circuit including the secondary windings of said pair of transformers, the primary of said output transformer, and said direct current source, said secondary windings connected in series opposition in said second circuit so that the cores of said pair of transformers are oppositely magnetized by the direct current flowin in said second circuit, a condenser in shunt to the secondary windings of said pair of transformers to time said second circuit to a harmonic of the frequency of the alternating current source, and an output circuit including the secondary winding of said output transformer.

ROY W. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,645,303 Slepian Oct. 11, 1927 1,829,419 Osnos Oct. 27, 1931 

